1. Field of the Invention
The present invention relates to a color image forming apparatus and, in particular, to a color image forming apparatus which has a plurality of pairs of optical scanning devices and corresponding image carriers, optical scanning being performed on each image carrier with a beam emitted from each optical scanning device to thereby form an image, or a color image forming apparatus which has an optical scanning device including a multi semiconductor laser and a plurality of image carriers, optical scanning being performed on the image carriers with a plurality of beams emitted from the optical scanning device to thereby form an image. The image forming apparatus is suitably applicable, for example, to a high speed laser printer apparatus, a plurality-drum type color copying machine or a digital color copying machine.
2. Description of the Related Art
Conventionally, in a color image forming apparatus such as a plurality-drum type color printer or a plurality-drum type color copying machine, a laser exposure device, that is, an optical scanning device has been used which provides a plurality of image forming sections corresponding to color components obtained through color separation with image data corresponding to the color components, that is, a plurality of beams.
Generally speaking, an optical scanning device comprises a semiconductor laser device serving as the light source, a first lens unit (collimator lens, cylindrical lens, etc.) for reducing the diameter of a beam emitted from the semiconductor laser device to a predetermined dimension, a light deflector for continuously deflecting and reflecting the beam whose diameter has been reduced by the first lens unit in a direction perpendicular to the direction in which the recording medium is conveyed, a second lens unit (Fxcex8 lens system) for forming an image at a predetermined position of the recording medium from the beam deflected and reflected by the light deflector, etc.
In known examples of such an optical scanning device, a plurality of optical scanning devices are arranged in correspondence with the image forming sections, or a multi-beam optical scanning device capable of providing a plurality of beams is arranged.
In an example of the multi-beam optical scanning device, lens units such as Fxcex8 lenses are arranged in a number corresponding to the number of beams, as disclosed in Japanese Patent Laid-Open No. 3-264970. Further, as disclosed in Japanese Patent Publication No. 2-20986, there is arranged in the vicinity of the photosensitive member (photosensitive drum) a cylindrical lens for causing a plurality of beams to impinge upon a single light deflector and to be condensed by a single fxcex8 lens (scanning lens) to correct any bend of the scanning line.
However, the above conventional multi-beam optical scanning devices have the following problems.
In the device disclosed in Japanese Patent Publication No. 2-20986, the beam impinges upon the fxcex8 lens obliquely, so that the scanning line is curved, and the curved scanning line is corrected by a cylindrical lens. However, the correction cannot be effected completely. When there are a plurality of incident beams, there exist a plurality of incident angles, and the scanning lines with different curvatures cause positional deviation on the surface of the photosensitive member.
In the device disclosed in Japanese Patent Laid-Open No. 3-264970, the number of lens units such as fxcex8 lens arranged corresponds to the number of beams. In the case of this arrangement, the plurality of beams pass the centers of the respective optical systems, so that curving of the scanning line is not easily generated. However, unless the accuracy of the optical systems is improved to an extreme degree, positional deviation in the scanning direction is generated on the surface of the photosensitive member due to errors in production. To avoid this, the lens accuracy is improved to an extreme degree, or a lens position adjusting mechanism is provided, resulting in the apparatus as a whole being complicated. Further, this leads to an increase in production cost.
It is a first object of the present invention to provide a color image forming apparatus of the type which has a plurality of pairs of optical scanning devices and image carriers, wherein each optical scanning device is appropriately constructed, whereby it is possible to prevent scanning positional deviation of each optical scanning device without having to improve the lens accuracy to an extreme degree.
It is a second object of the present invention to provide a color image forming apparatus of the type which has an optical scanning device including a multi semiconductor laser and a plurality of image carriers, wherein the optical scanning device is appropriately constructed, whereby it is possible to prevent scanning positional deviation without having to improve the lens accuracy to an extreme degree.
In accordance with the present invention, there is provided a color image forming apparatus of the type which has a plurality of sets of optical scanning devices and image carriers, in which beams emitted from the optical scanning devices re led to the surfaces of the corresponding image carriers, scanning being performed on the surfaces of the image carriers with the beams to form images of different colors on the surfaces of the image carriers, a color image being formed from the images formed on the surfaces of the plurality of image carriers,
wherein each of the plurality of optical scanning devices comprises
a laser unit having a semiconductor laser and a collimator lens,
a cylindrical lens consisting of a plastic lens material and adapted to form an image on the deflection surface of a light deflector from a beam emitted from the laser unit, and
an fxcex8 lens system having at least one plastic lens for forming an image on the surface of the image carrier from the beam deflected by the light deflector,
wherein at least one of the plastic lenses of the plurality of optical scanning devices is molded by a multiple cavity mold.
In particular, in each of the plurality of optical scanning devices, the laser unit, the cylindrical lens, and the fxcex8 lens system are held by a single plastic holding member, and the plastic holding member is molded by a multiple cavity mold.
In each of the plurality of optical scanning devices, the light deflector is also held by the plastic holding member.
The cavity combination of the plastic lens and the plastic holding member is specified, and, with another combination, the plastic lens is not attached to the plastic holding member.
The cavity combination of the plastic lens and the plastic holding member is constructed such that it can be recognized from the outside of each optical scanning device.
A plurality of optical scanning devices of the same cavity combination of the plastic lens and the plastic holding member are mounted in the apparatus main body.
The fxcex8 lens system has two plastic lenses, and the cavity combination of the two plastic lenses is specified, no attachment being possible with any other combination.
The cavity combination of the two plastic lenses constituting the fxcex8 lens system is constructed such that it can be recognized from the outside of each optical scanning device.
Optical scanning devices of the same cavity combination of the two plastic lenses constituting the fxcex8 lens system are mounted in the apparatus main body.
The plurality of optical scanning devices shares a light deflector.
Further, in accordance with the present invention, there is provided a color image forming apparatus of the type which has a plurality of sets of optical scanning devices and corresponding image carriers, and in which beams emitted from the optical scanning devices are led to the surfaces of the corresponding image carriers, scanning being performed on the surfaces of the image carriers with the beams to form images of different colors on the surfaces of the image carriers, a color image being formed from the images formed on the surfaces of the plurality of image carriers,
wherein each of the plurality of optical scanning devices has at least one plastic lens and a plastic holding member for holding at least one optical element, and at least one of the plastic lens and the plastic holding member is molded by the same cavity of the multiple cavity mold, and the cavity combination of the plastic lens and the plastic holding member is specified, the plastic lens not being attached to the plastic holding member with any other cavity combination.
In particular, the cavity combination of the plastic lens and the plastic holding member can be recognized from the outside of each optical scanning device.
A plurality of optical scanning devices of the same cavity combination of the plastic lens and the plastic holding member are mounted in the apparatus main body.
Each of the plurality optical scanning devices has a light deflector, which is held by the plastic holding member.
The plurality of optical scanning devices share a light deflector.
Further, in accordance with the present invention, there is provided a color image forming apparatus of the type which has a plurality of optical scanning devices including a multi semiconductor laser and a plurality of image carriers, and in which a plurality of beams emitted from the optical scanning devices are led to the surfaces of the corresponding image carriers, scanning being performed on the surfaces of the image carriers with the beams to form images of different colors on the surfaces of the image carriers, a color image being formed from the images formed on the surfaces of the plurality of image carriers,
wherein the plurality of optical scanning devices comprise
a laser unit having the multi semiconductor laser and a collimator lens,
a cylindrical lens consisting of a plastic lens material and adapted to form images on the deflecting surface of the light deflector from a plurality of beams emitted from the laser unit, and
an fxcex8 lens system having at least one plastic lens for forming images on the surfaces of the image carriers from the plurality of beams deflected by the light deflector, and
wherein at least one of the plastic lenses of the optical scanning device is molded in the same cavity of a multiple cavity mold.
In particular, in the plurality of optical scanning devices, the laser unit, the cylindrical lens, and the fxcex8 lens system are held by a single plastic holding member, and the plastic holding member is molded in the same cavity of a multiple cavity mold.
In the plurality of optical scanning devices, the light deflector is also held by the plastic holding member.
The cavity combination of the plastic lens and the plastic holding member is specified, and the plastic lens does not attach to the plastic holding member with any other combination.
The cavity combination of the plastic lens and the plastic holding member can be recognized from the outside of the optical scanning device.
In the plurality of optical scanning devices, the cavity combination of the plastic lens and the plastic holding member is the same.
The fxcex8 lens system has two plastic lenses, and the cavity combination of the two plastic lenses is specified, the attachment being impossible with any other combination.
The cavity combination of the two plastic lenses constituting the fxcex8 lens system can be recognized from the outside of the optical scanning device.
In the plurality of optical scanning devices, the cavity combination of the two plastic lenses constituting the fxcex8 lens system is the same.
Further, in accordance with the present invention, there is provided a color image forming apparatus of the type which has a plurality of optical scanning devices including a multi semiconductor laser and a plurality of image carriers, and in which a plurality of beams emitted from the optical scanning devices are led to the surfaces of the corresponding image carriers, scanning being performed on the surfaces of the image carriers with the beams to form images of different colors on the surfaces of the image carriers, a color image being formed from the images formed on the surfaces of the plurality of image carriers,
wherein the plurality of optical scanning devices have at least one plastic lens and a plastic holding member holding at least one optical element, wherein at least one of the plastic lens and the plastic holding member is molded in the same cavity of a multiple cavity mold, and wherein the cavity combination of the plastic lens and the plastic holding member is specified, and the plastic lens cannot be attached to the plastic holding member with any other combination.
In particular, the cavity combination of the plastic lens and the plastic holding member can be recognized from the outside of the optical scanning device.
In the plurality of optical scanning devices, the cavity combination of the plastic lens and the plastic holding member is the same.
The plurality of optical scanning devices have a light deflector, which is held by the plastic holding member.
Further, in accordance with the present invention, there is provided a color image forming apparatus of the type which has a plurality of sets of optical scanning devices and image carriers, and in which beams emitted from the optical scanning devices are led to the surfaces of the corresponding image carriers, scanning being performed on the surfaces of the image carriers to form images of different colors on the surfaces of the image carriers, a color image being formed from the images formed on the plurality of image carriers,
wherein each of the plurality of optical scanning devices comprises
a laser unit,
a light deflector for deflecting the beam emitted from the laser unit, and
a lens system having at least one plastic lens for forming an image on a predetermined surface from the beam emitted from the laser unit, and
wherein at least one of the plastic lenses of the plurality of optical scanning devices is molded in the same cavity of a multiple cavity mold.
In particular, in each of the plurality of optical scanning devices, the laser unit and the lens system are held by a single plastic holding member, and the plastic holding member is molded in the same cavity of a multiple cavity mold.
In each of the plurality of optical scanning devices, the light deflector is also held by the plastic holding member.
The laser unit has a multi semiconductor laser emitting a plurality of beams.
Further, in accordance with the present invention, there is provided a color image forming apparatus of the type which has an optical scanning device including a light source portion emitting a plurality of beams and a plurality of image carriers, and in which a plurality of beams emitted from the optical scanning device are led to the surfaces of the corresponding image carriers, scanning being performed on the surfaces of the image carriers with the beams to form images of different colors on the surfaces of the image carriers, a color image being formed from the images formed on the surfaces of the plurality of image carriers,
wherein the optical scanning device comprises
a light source portion,
a light deflector for deflecting a plurality of beams emitted from the light source portion, and
a lens system having at least one plastic lens for effecting image formation on a predetermined surface with the plurality of beams emitted from the light source portion,
wherein there are provided a plurality of said lens systems in correspondence with the plurality of beams, and wherein at least one of the plastic lenses of the lens systems is molded in the same cavity of a multiple cavity mold.
Further, in accordance with the present invention, there is provided a color image forming apparatus of the type which has an optical scanning device including a multi semiconductor laser and a plurality of image carriers, and in which a plurality of beams emitted from the optical scanning device are led to the surfaces of the corresponding image carriers, scanning being performed on the surfaces of the image carriers with the beams to form images of different colors on the surfaces of the image carriers, a color image being formed from the images formed on the surfaces of the plurality of image carriers,
wherein the optical scanning device comprises
a laser unit having a multi semiconductor laser and a collimator lens,
a light deflector for deflecting a plurality of beams emitted from the laser unit,
a cylindrical lens consisting of a plastic lens material and adapted to effect image formation on the deflection surface of the light deflector from the plurality of beams emitted from the laser unit, and
and an fxcex8 lens system having at least one plastic lens for effecting image formation on a predetermined surface from the plurality of beams deflected by the light deflector,
wherein there are provided a plurality of said fxcex8 lens systems in correspondence with the plurality of beams, and wherein at least one of the plastic lenses of the fxcex8 lens systems is formed in the same cavity of a multiple cavity mold.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.